The rivers originating in the Himalayas carry a large amount of sediment, causing erosion of the banks in the upper reaches and over-topping in the lower segments.

The most flood-prone areas are the Brahmaputra, Ganga and Meghana basins in the Indo-Gangetic-Brahmaputra plains in north and northeast India, which carry 60 per cent of the nation's total river flow.

The Ganga-Brahmaputra-Meghana basin is one of the largest in the world. In India it is spread over 15 states and covers a geographical area of 1.75 million square kms of which 75.8 per cent lies in India. About 47 per cent of India's population resides in the basin.

The basin can be broadly divided into four regions: the Himalayan zone, the plains, the hilly tracts of the northeast, and the southwest hilly tracts along the fringe states in India.

The other flood-prone areas are the northwest region of the west-flowing rivers like the Narmada and Tapti, and central India and the Deccan plateau with major east-flowing rivers like the Mahanadi, Krishna and Cauvery.

Notwithstanding flood policy and flood control schemes, flood damage is increasing, with larger populations subjected to distress in increasing flood-prone areas. The locus has shifted away from the Gangetic belt. The distribution of damage is widespread, with the worst-hit being Andhra Pradesh, Karnataka, Kerala and Tamil Nadu in the south; Maharashtra, Gujarat and Rajasthan in the west; Uttar Pradesh in the north; and Bihar and West Bengal in the east.

The flood problem has become chronic in 10 out of 19 states exposed to floods. Of these 10 only four -- Assam, Bihar, Punjab and West Bengal -- lie in the Gangetic flood plains; the other six are in peninsular India or in the Himalayan ranges. In Orissa, Kalahandi, Koraput, Bolangir, Malkangiri, Phulbani and Rayagada districts have witnessed recurring floods since 1965 with the administration taking steps to mitigate the consequences of these floods.

Ironically the first three districts of Orissa mentioned above are also those which face recurring drought.

Around 40 million hectares of land in the country are subject to floods and an average of 18.6 million hectares of land are affected annually. The annual average cropped area affected is approximately 3.7 million hectares. The average annual total damage to crop, houses and public utilities during the period 1953-95 was about Rs 9,720 million. The maximum damage was Rs 46,300 million in 1988.

Major rivers of India Click here to enlarge map

The army had to be summoned to the aid of civil authorities in six of the 19 states affected by floods.

The annual average flood damage based on data from 1953-94 is as follows:

• Land area affected------- ----------7.56 million hectare
• Population affected-----------------32.03 million
• Human lives lost--------------------1,504
• Livestock lost-------------------------96,713
• Houses damaged------------------11,683 (or in money value -- Rs 1.37 billion)
• Crop damaged-----------------------Rs 4.6 billion
• Public utilities damaged-----------Rs 3.77 billion
  

Forecasting
The Central Water Commission has a flood forecasting system covering 62 major rivers in 12 states and one union territory with 157 stations for transmission of flood warnings on real-time basis.

In 1995, 8,566 forecasts were issued with a percentage accuracy of 95 per cent. There are also 55 hydro-meteorological stations in the 62 river basins. VHF/HF wireless communication system is used for data collection with micro-computers at the forecasting centres. Hydrological models are increasingly used for inflow and flood forecasting and the forecasts are communicated to the administrative and engineering departments for dissemination.

Flood mitigation
Between 1957 and 1995 Rs 4,000 crore was invested in structural methods of flood mitigation. This covered the construction of new embankments (16,200 kms), drainage channels (32,000 kms) and raising 4,700 critical villages above the flood level which ensured protection to an estimated 14.4 million hectares.

Multi-purpose dams and reservoirs such as the Damodar valley systems in eastern India, Hirakud dam in Orissa and the Bhakra on the River Sutlej (Punjab) enable flood moderation. Flood moderation was one of the objectives in the construction of these dams. The Damodar valley system has a flood absorption capacity of 1,867 mcm, which moderates probable floods of 28,300 cusecs to 7,075 cusecs in the valley.

The River Valley Project (RVP) in the catchments of major rivers is a scheme for soil conservation. This consists of control of premature siltation of multi-purpose reservoirs and checking degradation. The scheme covers 581 watersheds in 27 catchments in 17 states.

The National Policy of 1954 underlined the importance of multipurpose reservoirs to moderate floods, but supplemented it with structural measures consisting of the construction of embankments, detention basins, improvements, and construction of drainage channels, along with anti-erosion and river training works. It emphasised the need for taking up flood protection works in a systematic and planned manner and outlined a time-bound plan of action.

The increasing trend in flood damage since the 1970s led the central government to initiate steps for the development of flood plains in a regulated manner. During the decades from the 1960s to 1980s there was a dependence on structural measures but as these alone did not yield the desired results, non-structural measures such as flood forecasting, flood plain zoning, flood proofing of the civic amenities of the affected villages, changing the cropping pattern and public participation in flood management works are being encouraged. These measures are also cost- and time-effective.

District contingency plans deal with the different phases of flood management.

The Brahmaputra river system
The River Brahmaputra that flows from the Himalayas is around 2,900 kms long: it flows 1,000 kms through Tibet, 700 kms in Assam and the remaining in Bangladesh. It is surrounded by the Himalayas to the north, the Patkai to the east, the Karbi, North Cachar, Khasi and Garo hills to the South. The catchment area of the river measures 174,500 sq kms.

There are 34 major tributary rivers of the Brahamaputra, which are characterised by steep slopes, easily erodible catchment soil, heavy monsoon precipitation and high seismic instability. The Brahmaputra valley and its adjoining high lands constitute a highly active seismic region. Earthquakes measuring upto 8.7 on the Richter scale occurred here in 1897 and 1950.

Floods in Brahmaputra valley, Assam
Flood is a common phenomenon in the Brahmaputra valley. All the districts of the Brahmaputra valley in Assam are inundated almost every year. An area of 30 lakh hectares out of 78 lakh hectares, ie about 45 per cent of Assam's total area, is flood-prone. The flood discharge varies from 5 lakh cusecs to 7.5 lakh cusecs. It spreads to a width of 10-16 kms. At present the total length of embankments along the Brahmaputra is 934 kms and 2,400 kms along various tributaries. It provides protection to an area of 13.27 lakh hectares out of the total flood-prone area of 30 lakh hectares.

The main causes for the high incidence of floods are:

• Very heavy rains in the region
  
• Narrowness of the Brahmaputra valley with a maximum width of about 81 kms surrounded by hills
  
• Deposits of huge quantities of silt from these hills following heavy rain, because of which riverbeds have risen to a great extent, which reduces the capacity of the river
  
• Earthquakes change the course of the river
  
• Very high population pressure due to migration from Bangladesh and other states of India, to originally uninhabited flood-prone areas

An important characteristic of the floods is that there is no seasonality in its occurrence. It has been observed that floods have occurred outside the traditionally observed June-September period.

As much as 73.7 per cent of the annual aggregate precipitation of 400 million hectare metres are received during the southwest monsoon months of June to September. The erratic behaviour of the monsoon causes periodical droughts in both low (less than 750 mm) and medium (750-1125 mm) rainfall regions, which constitute 68 per cent of the total area.

Analysis of 100 years of rainfall behaviour has revealed that the frequency of occurrence of below-normal rainfall in arid, semi-arid and sub-humid areas is 54-57 per cent, while severe and rare droughts occur once every eight to nine years in arid and semi-arid zones.

In the semi-arid and arid climatic zones about 50 per cent of the severe droughts impact around 76 per cent of the area. In this region, rare droughts of severe intensity occurred on an average once in 32 years and almost every third year was a drought year.

The impact of drought varies from year to year. India faced droughts in 1966-67, 1972-73, 1979-80 and 1986-87. In each case, food production fell below the national average. There were large-scale losses through starvation, depletion of assets and livestock and high mortality.

The 1987 drought, which was one of the worst droughts of the 20th century, with overall rainfall deficiency of 19 per cent, affected 58-60 per cent of cropped area and a population of 285 million. Over 267 districts and 166 million people were recorded drought-affected.

In 1996, 10 meteorological sub-divisions received deficient rainfall from the northeast monsoon; 67 districts had below-normal rainfall from the northwest monsoon. The northeast monsoon caused floods in parts of Gujarat, but Orissa, Madhya Pradesh, Maharashtra and other parts of Gujarat were drought-stricken.

Districts with deficient rainfall or facing drought-like situation (around May-June 2001)

Madhya Pradesh: Badwani, Balaghat, Betul, Bhind, Chhatarpur, Chhindwara, Damoh, Dhar, Dindori, Indore, Jabalpur, Jhabua, Katni, Khandwa, Khargone, Mandla, Mandsour, Morena, Narsinghpur, Neemuch, Panna, Rajgarh, Ratlam, Satna, Seoni, , Shahdol, Shajapur, Sheopur, Sidhi, Tikamgarh, Ujjain, Umaria

Gujarat: Ahmedabad, Amreli, Anand, Banaskantha, Bharuch, Bhavnagar, Dahod, Gandhinagar, Jamnagar, Junagadh, Kheda, Kutch, Mehsana, Narmada, Panchmahal, Patan, Porbandar, Rajkot, Sabarkantha, Surat, Surendranagar, Vadodara

Rajasthan: Ajmer, Alwar, Banswara, Baran, Barmer, Bharatpur, Bhilwara, Bikaner, Bundi, Chittor, Churu, Dausa, Dungarpur, Ganganagar, Hanumangarh, Jaipur, Jaisalmer, Jalore, Jhalawar, Jhunjhunu, Jodhpur, Karauli, Kota, Nagaur, Pali, Rajsamund, Sawai Madhopur, Sikar, Sirohi, Tonk, Udaipur

Maharashtra: Ahmednagar, Akola, Amravati, Aurangabad, Bhandara, Buldhana, Chandrapur, Dhule, Gadchiroli, Gondia, Jalgaon, Jalna, Nagpur, Nanded, Nandurbar, Nasik, Pune, Raigad, Satara, Thane, Vashim, Wardha, Yevatmal, Sangli, Solapur, Latur

Orissa: Angul, Boudh, Balasore, Bargarh, Bolangir, Deogarh, Dhenkanal, Ganjam, Gajapali, Jagatsinghpur, Jajpur, Jharsuguda, Keonjhar, Kalahandi, Kandhamal, Khurda, Kendrapara, Koraput, Mayurbhanj, Malkangiri, Nuapada, Navarangpur, Nayagarh, Puri, Rayagada, Sonepur, Surendergadh, Sambalpur

Chattisgarh: Bilaspur, Durg, Dhamtari, Jaspur, Janjgir, Kanker, Kawardha, Korba, Mahasamund, Raigarh, Raipur, Rajnandgaon

Himachal Pradesh: Bilaspur, Chamba, Hamirpur, Kangra, Kinnaur, Kullu, Lahaul & Spiti Manali, Shimla, Sirmaur, Solan, Una

Uttaranchal: Tehri Garhwal

Drought Forecasting
The IMD has divided the entire country into 35 meteorological sub-divisions. It issues weekly bulletins on rainfall indicating normal, excess and deficient levels and also the percentages of departure from the normal.

The CWC monitors the levels of 60 major reservoirs with weekly reports of reservoir levels and corresponding capacity for the previous year and the average of the previous 10 years.

Similar monitoring of smaller reservoirs by the irrigation departments of state governments gives advance warning of hydrological droughts with below-average stream flows, cessation of stream flows and decrease in soil moisture and groundwater levels.

Based on the input from IMD and CWC and the information on crop situations received from the local sources, the National Crop Weather Watch Group monitors the drought conditions. Remote sensing techniques are also used for monitoring drought conditions based on vegetative and moisture index status.

Drought mitigation
India has undertaken irrigation development by harnessing water through medium reservoirs, developing traditional systems of tanks and exploiting groundwater. The average annual investment on major and medium-term irrigation projects rose from Rs 750 million in the First Five Year Plan to Rs 25,000 million in the Eighth Five Year Plan creating a total potential of 38 million hectares.

The irrigation potential has not been fully utilised for want of on-farm development works like field channels, land levelling, field drains and absence of appropriate system of water distribution to ensure appropriate water management. The Government of India operates a command area development programme (CADP) to strengthen water management capabilities and enhance the effectiveness of irrigation water application.

The Drought Prone Areas Programme (DPAP) directed at drought-prone areas is under implementation since 1973 in 149 districts in 14 states.

The Desert Development Programme (DDP) started in 1977-78 aims at controlling the process of desertification and mitigating the adverse effects of drought in the desert areas through afforestation, sand-dune stabilisation, shelter belt plantation, grassland development and soil and moisture conservation. It is being implemented in 36 districts in seven states.

Seventy per cent of India's cultivated land is in the rainfed areas, which often suffer reverses in agricultural production and face drought conditions. A programme titled National Watershed Development Project for Rainfed Areas (NWDPRA) has been devised and is under implementation. This programme includes development measures for all the spatial components of watersheds ie arable land, non-arable land and drainage lines as one organic geo-hydrological entity.

The objective is to achieve conservation of rainwater, control of soil erosion, regeneration of green cover and promotion of dry land farming systems including horticulture, agro-forestry, and pasture development and livestock management as well as household production systems.

There are large areas of degraded land of over 100 million hectares in the country, which through basic water and soil conservation measures and plantation and protection work could be reclaimed. Protection, regeneration and restoration of the degraded land can reduce the pressure on remaining land, forests and pastures. A National Wasteland Development Board has been constituted for promoting integrated wasteland development.

The National Forest Conservation Act (1980) aims to protect and prevent the erosion of forest cover.

Natural disasters, particularly droughts, create unemployment and under-employment problems in the rural areas. The Jawahar Rozgar Yojana (JRY) is the largest programme in the country aimed at generating additional gainful employment for the unemployed and under-employed men and women in rural areas. The Employment Assurance Schemes (EAS) provide employment opportunities mostly in drought-prone areas.

The entire east coast is vulnerable to cyclones with varying frequency and intensity. India has a very long coastline of 7,516 kms exposed to tropical cyclones arising mainly in the Bay of Bengal and Arabian Sea.

The states most exposed to cyclone-related hazards, including strong winds, floods and storm surges, are West Bengal, Orissa, Andhra Pradesh and Tamil Nadu along the Bay of Bengal.

Along the Arabian Sea on the west coast, the Gujarat and Maharashtra coasts are more vulnerable compared to the southern part.

The frequency of tropical cyclones is the greatest in the Bay of Bengal and Arabian Sea as compared to other cyclone-prone areas in the world. Also the cyclones are mostly moderate in intensity, but the storm surges increase in intensity when they cross the shoreline.

On an average, about five to six tropical cyclones form in the Bay of Bengal and Arabian Sea every year, out of which two to three may be severe. More cyclones form in the Bay of Bengal than in the Arabian Sea; the ratio is 4:1. Cyclones are most deadly when crossing the coast bordering the north of the Bay of Bengal, coastal areas of Andhra Pradesh, Orissa, West Bengal and Bangladesh, mainly because of the serious storm-surge problem in this area.

The eastern coastline is more prone to cyclones as around 80 per cent of the total cyclones generated in the region hit there. Cyclone formations require warm seas and still air. In the Bay of Bengal, these are the conditions that normally occur in the months of April-May and October-December. Cyclones strike here in May-June and October -November with the monsoon's onset and retreat.

Analysis of cyclone events during the last 100 years (from 1891 to 1991) reveals that as against 117 cyclones of varied intensity formed in the Arabian Sea, 442 cyclones were formed in the Bay of Bengal.

The impact of these cyclones is confined to the coastal districts, the maximum destruction being within 100 kms from the centre of the cyclones and on either side of the storm track.

The principal dangers from a cyclone are: (i) gales and strong winds; (ii) torrential rain and (iii) high tidal waves (also known as 'storm surges'). Most casualties are caused by coastal inundation by tidal waves and storm surges.

The worst devastation takes place when and where the peak surge occurs at high tide.

Stretches along the Bay of Bengal coastline have the world's shallowest waters but the relatively dense population and poor economic condition complicate the situation.

The population density in some of the coastal districts is as high as 670 persons per square km compared to the state average of 268 persons per square km. Between 1877 and 1977, 20 per cent of cyclones from the Bay of Bengal crossed the coast in November and 18 per cent in May; 337 crossed the east coast of India and Bangladesh between latitudes 8 degrees N and 22 degrees N.

The next most cyclone-prone area is the Krishna delta in Andhra Pradesh on the east coast of peninsular India at latitude 15-16 degrees N. The most vulnerable districts are Nellore, Krishna, Srikakulam and East Godavari in Andhra Pradesh.

Andhra Pradesh was hit by a severe cyclonic storm in May 1990. The wind speed recorded was about 240-250 kmph with 5-6-metre-high storm surges. The area all along the coast of Krishna and Guntur districts was affected severely by the storm which was accompanied by gales and heavy rainfall. Other areas were affected by flooding due to heavy rainfall. The cyclone affected nine of the total 23 districts, while the number of villages affected was 5,923. The cyclone killed 928 persons and around 24,000 cattle. A total of about of 7.8 million people were affected by the cyclone. About 827,100 houses were partially damaged while 569,000 were completely destroyed. More than 500,000 hectares of agricultural and horticultural land was affected. Total damage to property was worth Rs 125 million.

Cyclone tracking is done through INSAT satellite and 10 cyclone detection radars. Warning is issued to cover ports, fisheries and aviation departments. The warning system provides for a cyclone alert of 48 hours and a cyclone warning of 24 hours.

There is a special Disaster Warning System (DWS) for dissemination of cyclone warning through INSAT satellite to designated addresses at isolated places in local languages.

Much headway has been made in cyclone warning. This is evidenced from the difference in loss suffered during cyclones, which hit the Andhra Pradesh coast in 1977 and 1990. The cyclones were accompanied by high storm surges of high intensity. The number of deaths in 1977 was over 10,000 whereas the loss of human lives in 1990 was less than 1,000. Timely warnings issued by the IMD enabled the administration in evacuating and transporting over half a million people from the affected areas.

A constant watch is kept on the Arabian Sea and the Bay of Bengal for the likely genesis of tropical cyclones with the help of satellite imagery, particularly those from the Indian geostationary satellite, INSAT. Data from ships and ocean buoys is also very valuable.

When the systems come nearer to the Indian coastline, a chain of cyclone detection radars, that cover the entire coastal belt, set up by IMD monitor their subsequent development and movement.

The likely movement of the storms is predicted with the help of track prediction models and by reference to past climatology, which has been built up using 125 years of cyclone data.

Cyclone warning centres
Cyclone warnings are provided by the India Meteorological Department from the Area Cyclone Warning Centres (ACWC) at Calcutta, Chennai and Mumbai and Cyclone Warning Centres (CWC) at Vishakhapatnam, Bhubaneshwar and Ahmedabad.

The cyclone warning process is coordinated by the weather central in the office of DDGM (weather forecasting) at Pune and the Northern Hemispheric Analysis Centre at New Delhi.

The division provides Doordarshan and AIR stations at New Delhi with cyclone warning bulletins for inclusion in the national broadcast/telecast. Information on cyclone warnings are furnished on a real time basis to the control room set up in the ministry of agriculture, government of India, besides other ministries and departments of the government.

Cyclone warnings are disseminated through a variety of communication media, such as radio, television, print media, telephones, fax, telex, telegrams and police wireless network.

A specially designed cyclone warning dissemination system, which works via the INSAT satellite, provides area-specific service even when there is a failure of conventional communication channels.

Warnings are issued for general public, fishermen, farmers and different categories of users such as central and state government officials responsible for disaster mitigation and relief, industrial and other establishments located in the coastal areas, railways, aviation, communications and power authorities.

Regional specialised meteorological centre

NHAC, New Delhi, has been designated as the regional specialised meteorological centre for tropical cyclones. It is one of the five such centres recognised by the WMO under a global system for monitoring tropical cyclones.

Cyclone mitigation

Governmental measures to deal with cyclones consist of building of cyclone shelters, afforestation in coastal areas, etc.

The Government has undertaken reconstruction projects in areas affected by major calamities the purpose of which is also being prepared for possible future calamities.

The Cyclone Reconstruction Project implemented in coastal Andhra Pradesh during 1990-93 apart from consisting of building housing and public infrastructure, drainage and rural water supply, included such mitigation efforts as expanding road and communication network, planning of shelter belt plantation and building up of cyclone shelters.

The peninsular part of India comprises stable continental crust regions, which are considered stable as they are far away from the tectonic activity of the boundaries. Although these regions were considered seismically least active, an earthquake that occurred in Latur in Maharashtra on September 30, 1993 of magnitude 6.4 in the Richter scale caused substantial loss of lives and damage to infrastructure.

Based on earthquake occurrence data and the country's seismogenic features, a new seismological map of India was standardised three years after the 1967 Koyna earthquake (M6.5), the strongest ever in the Deccan peninsula. The 1993 Latur earthquake (M6.4) and the 1997 Jabalpur shock (M6) confirmed the seismicity of the Deccan plateau.

Earthquake warning

Earthquakes, among the most dangerous and destructive natural hazards are also the least easy to predict. Warnings against it or preparations against physical destruction are difficult. Around 50 to 60 per cent of total area is vulnerable to seismic activity of varying intensities.

IMD is the nodal agency of the Government of India dealing with warning and monitoring. The seismology division of IMD is located at New Delhi and its activities are:

• Attends to all enquiries pertaining to seismology
• Is responsible for publication of national seismic data and exchange of seismic data with national and international agencies
• Assists various national organisations in seismic studies and maintains liaison with international bodies
• Supplies seismic co-efficients for design of large and small dams to the project authorities

Monitoring earthquakes in and around India

IMD at present maintains 45 national seismological observatories. In addition, there are nine observatories for special studies in north India and three mobile observatories in and around Delhi. Ten observatories in peninsular India were upgraded to GSN Standard duing 1996-97.

A National Seismological Data Base Centre (NSDC) along with a central receiving station (CRS) has been established at New Delhi to receive and archive seismic data. NSDC receives both digital and analog data in near real time mode.

During early 1999, 12 more seismological observatories have been upgraded with Broad Band Digital seismographs.

NSDC is responsible for quick event determination and dissemination of the information in an operational mode, and archiving all relevant data for further analyses.

Earthquake mitigation

Much loss of life during the past earthquakes has occurred due to the collapse of traditional buildings of clay, stones and bricks. The bulk of the housing in India consists of such buildings.

Studies on this problem were started at the University of Roorkee in 1960. Very useful recommendations regarding upgrading of such buildings were available in the Geological Survey of India Memoirs on the 1934 Bihar earthquake and 1935 Quetta (now in Pakistan) earthquake. These efforts resulted in the preparation and publication of IS:4326 in 1976.

After the Koyna earthquake (Maharashtra), research efforts were devoted to shake-table tests on larger scale specimens for checking the validity of the reinforcing recommendations of IS:4326 and also to further refine the analysis procedures.